Fix unexpected failures in CopyPackagesToSplitFolders when files exists

build/repo.targets

@@ -39,10 +39,7 @@
 
     <RepoTasks.DownloadNuGetPackages
       Packages="@(ExternalDependency->WithMetadataValue('Mirror', 'true'))"
-      DestinationFolder="$(IntermediateMirrorPackageDir)">
-
-      <Output TaskParameter="Files" ItemName="MirroredPackageFile" />
-    </RepoTasks.DownloadNuGetPackages>
+      DestinationFolder="$(IntermediateMirrorPackageDir)" />
   </Target>
 
   <Target Name="CleanUniverseArtifacts">
@@ -209,17 +206,14 @@
     <ItemGroup>
       <PackageArtifactFile Include="$(BuildDir)*.nupkg" Exclude="$(BuildDir)*.symbols.nupkg" />
       <ExternalDependencyPackage Include="@(ExternalDependency->WithMetadataValue('Mirror', 'true'))" Category="mirror" />
-      <MirroredPackageFile Include="$(IntermediateMirrorPackageDir)*.nupkg" />
+      <_MirroredPackageFiles Include="$(IntermediateMirrorPackageDir)*.nupkg" />
     </ItemGroup>
 
-    <RemoveDuplicates Inputs="@(MirroredPackageFile)">
-      <Output TaskParameter="Filtered" ItemName="_MirroredPackageFiles" />
-    </RemoveDuplicates>
-
     <RepoTasks.CopyPackagesToSplitFolders
       Packages="@(PackageArtifact);@(ExternalDependencyPackage)"
       Files="@(PackageArtifactFile);@(_MirroredPackageFiles)"
-      DestinationFolder="$(ArtifactsDir)" />
+      DestinationFolder="$(ArtifactsDir)"
+      Overwrite="true" />
   </Target>
 
   <Target Name="VerifyCoherentVersions" DependsOnTargets="ResolveRepoInfo">

build/tasks/CopyPackagesToSplitFolders.cs

@@ -28,6 +28,8 @@ namespace RepoTasks
         [Required]
         public string DestinationFolder { get; set; }
 
+        public bool Overwrite { get; set; }
+
         public override bool Execute()
         {
             if (Files?.Length == 0)
@@ -79,9 +81,14 @@ namespace RepoTasks
 
                 var destFile = Path.Combine(destDir, Path.GetFileName(file.ItemSpec));
 
-                Log.LogMessage($"Copying {file.ItemSpec} to {destFile}");
+                if (!Overwrite && File.Exists(destFile))
+                {
+                    Log.LogError($"File already exists in {destFile}");
+                    continue;
+                }
 
-                File.Copy(file.ItemSpec, destFile);
+                Log.LogMessage($"Copying {file.ItemSpec} to {destFile}");
+                File.Copy(file.ItemSpec, destFile, Overwrite);
                 expectedPackages.Remove(identity.Id);
             }
 
@@ -97,7 +104,7 @@ namespace RepoTasks
                 return false;
             }
 
-            return true;
+            return !Log.HasLoggedErrors;
         }
     }
 }